What's wrong with this rewrite rule?

Hello, I've been messing with a certain rewrite rule for about 30 minutes now and it's driving me insane. I've got plenty of other rewrite rules working perfectly. Here is the rule in question. RewriteRule ^detail\.asp\?product_id=([\w-]+)$ product.php?id=$1 The URL I'm testing this with is: http://www.nonlethal.com/detail.asp?product_id=bh35wg00od This is to stop 404's from a legacy product that has these old links in it. i.e. "detail.asp?product_id=" was what the old site used, "product.php?id=" is what the new site uses. Anyone see what I'm missing? Chris.